I have a question regarding adding non-DMG abilities to a weapon. The primary spell in question here in Enervation. Now the DMG provides rules to add the spell to a magic item as a base price but as per the article at the begining of this year by Skip Williams, any spell added which increases it's combat (hit or damage done) should be a Weapon Bonus. Enervation would do 1d4 negative levels of damage extra but I can not seem to find how you determine what the bonus should be.